The invention relates to a method and apparatus for melting, smelting, boiling, vaporizing, fuming, and/or charring primary or secondary (recycled) organic materials from natural, commercial or societal sources for the purpose of extracting volatile organic vapors and producing a carbon rich residual char. The invention is particularly applicable for selectively and controllably producing either an unreformed pyrolysis gas rich in condensable hydrocarbon gases or, more particularly, a reformed synthesis gas rich in hydrogen and carbon monoxide and containing little or no condensable hydrocarbon gases, for use as a primary feedstock in chemical processes or as a fuel.
It has been known for many years that thermal processing (pyrolysis) of organic-based primary or secondary raw materials can be used to recover petroleum-like distillates (syncrude), synthesis gas (syngas) and a carbon enriched residue. For example, since the late 1700's, methods and apparatus, such as traveling grates, stoker grates, rotary kilns, shaft furnaces, beehive ovens, coke ovens, moving bed and static bed retorts, fluid bed reactors, pneumatic reactors, auger reactors, drag chain reactors, rotary hearth reactors, and the like, have been used for pyrolysis and/or gasification of coal and other raw materials that contain carbon, hydrocarbons and/or cellulose. However, after the discovery of large quantities of natural gas, and before the "energy crisis" of the mid-1970's, pyrolysis of raw materials was primarily used to produce charcoal or coke and, only secondarily, the by-product distillates and synthesis gases which were variously known as "producer gas", "water gas", "carburetted water gas", "blue gas", "coke oven gas" and "blast furnace gas". The commercial uses of these by-product gases were generally very limited unless it was possible for them to be used internally to supply heat for associated processes, to generate steam for a nearby power plant, or to be easily pipelined for use in public street lights. Thus, due primarily to unfavorable economy-of-scale and/or market location, very little use was made of these gases for chemical purposes in petroleum-rich areas of the world. The combination of rising environmental concerns in the 1960's concerning the safe disposal of domestic and industrial organic toxic wastes, and the energy crisis in the 1970's, stimulated interest in the development of new technologies for pyrolysis and gasification of organic waste materials that would concomitantly produce synthesis gases and/or distillates of syncrude gases usable as substitutes for petroleum.
The methods used for pyrolysis and/or gasification processes generally have in common the heating of raw feed materials that contain carbon, hydrocarbons and/or cellulose compounds to high temperatures in an oxygen starved or oxygen controlled atmosphere. Pyrolysis processes, by design, require the process to be practiced in some type of air tight indirectly heated retort in order to prevent contamination of the resulting pyrolysis gases with nitrogen, carbon dioxide and water vapor, which could result due to leakage or the entry of uncontrolled air into the retort. Consequently, in order to achieve an acceptable and efficient level of heat transfer via indirect heating, it is common to construct such vessels with high alloy metals that do not require insulation and/or refractory protection. However, such metallic retorts, or other vessels without insulation and/or refractory, have an inherent temperature limit to which they can be repeatedly heated without suffering damaging structural deterioration. The operational temperature limit reduces the ability of indirectly heated retorts to efficiently heat the feed material above about 500.degree. C. to 650.degree. C.
While organic feed material can be pyrolyzed at these temperatures, heating restrictions inherent in the design of indirectly heated retorts places limitations on their size which, in turn, can critically limit both efficiency and economics. In order to convert the pyrolysis gas formed in these retorts into a stable non-condensable gas suitable for use as fuel or as a primary feedstock for chemical processes, it is necessary to heat the hydrocarbon vapors to temperatures between 700.degree. C. and 1000.degree. C. and to crack and/or dissociate them to form synthesis gas in a secondary processing system downstream of the pyrolysis retort. Further, the resulting pyrolysis gas from such retorts contains a large quantity of complex hydrocarbons that recondense when the gases are cooled below their vapor temperature. Thus, downstream gas-processing equipment must be provided for handling the condensation of hydrocarbon liquids and separating these from the remaining synthesis gas.
U.S. Pat. No. 5,425,792 discloses a process in which gasification of organic materials is carried out in a primary tumbling reactor with an interior refractory lining, and having a single reaction zone and an oxygen/fuel burner with a high flame temperature positioned only at the discharge end of the reactor. The process burner inside the reactor is balanced in positioning and capacity in such a way that it is capable of delivering the necessary heat for thermally decomposing the organic materials to evolve pyrolysis gases containing complex hydrocarbons and to thermally crack and dissociate the evolving gases (at 650.degree. to 800.degree. C.) by the products of combustion of the burner to produce a synthesis gas containing less than about two percent by volume of gases with a molecular structure having more than two carbon atoms. However, in order to further reform methane and two carbon or greater (+C.sub.2) hydrocarbons or carbon dust particles remaining in the synthesis gas, to produce a higher quality synthesis gas that is richer in carbon monoxide and hydrogen, the process requires a secondary "finishing" reactor with a secondary finishing gas (burner) stream positioned downstream from the primary reactor. The process is limited to no more than 10% excess oxygen relative to the molar content of the burner injected fuel.
In view of the foregoing, there is still a need to provide a safe, efficient and more versatile process and apparatus for pyrolysis and/or gasification of primary and secondary (recycled) organic materials to produce either an unreformed pyrolysis gas rich in condensable hydrocarbon gases, or a reformed synthesis gas rich in carbon monoxide and hydrogen gases and containing little or no condensable hydrocarbon gases.